Bismuth borate glass encapsulant for LED phosphors

ABSTRACT

Embodiments are directed to glass frits containing phosphors that can be used in LED lighting devices and for methods associated therewith for making the phosphor containing glass frit and their use in glass articles, for example, LED devices.

This is a divisional application and claims the benefit of priorityunder 35 U.S.C. § 120 of U.S. application Ser. No. 14/665,634 filed Mar.23, 2015, now U.S. Pat. No. 9,624,124, which is a divisional applicationand claims the benefit of priority under 35 U.S.C. § 120 of U.S.application Ser. No. 13/852,048 filed Mar. 28, 2013, now U.S. Pat. No.9,011,720, which in turn claims the benefit of priority under 35 U.S.C.§ 119 of U.S. Provisional Application Ser. No. 61/618,194 filed on Mar.30, 2012, the contents of which are relied upon and incorporated hereinby reference in their entirety.

FIELD

The disclosure is directed to glass frits containing phosphors that canbe used in LED lighting devices and for methods associated therewith formaking the phosphor containing glass frit and their use in glassarticles, for example, LED devices.

TECHNICAL BACKGROUND

Yellow and red phosphors can be used to create white light emittingGaN-based LEDs. These phosphors are typically encapsulated by asilicone. The latter material tends to yellow or darken over time.Moreover, due to its lower refractive index relative to that of thephosphor, the resultant backscatter degrades the LED efficiency.Previous work has demonstrated the efficacy of a glass encapsulant withlow characteristic temperatures, particularly one that is index-matchedto the phosphor as described in commonly-assigned U.S. patentapplication Ser. No. 13/281,671 filed on Oct. 26, 2011, the content ofwhich is incorporated herein by reference in its entirety. However, theindex-matched glasses developed to date for this application havetypically contained Pb, which has since been deemed an inadmissiblecomponent.

Accordingly, there is a need for comparable Pb-free encapsulant glassesthat can be index-matched to the LED phosphors and that can function asa sealing frit at temperatures below the upper use limit of thephosphors.

SUMMARY

This disclosure is directed to the encapsulation of phosphors in a glassmaterial that does not degrade or become brittle over time, is thermallyrobust and has a better refractive index match to the phosphor, reducingefficiency-robbing backscatter of blue light back into the LED.

One embodiment is an article comprising a glass layer, wherein the layercomprises a glass comprising Bi₂O₃ and at least 30 mol % B₂O₃; and atleast one phosphor, wherein the layer is a fired mixture of a fritcomprising the Bi₂O₃ and B₂O₃ and the at least one phosphor, and whereinthe layer is Pb free.

Another embodiment is a method for making a glass article, the methodcomprising:

-   -   providing a glass composition comprising Bi₂O₃ and B₂O₃;    -   melting the composition and forming the melted composition into        a glass;    -   grinding the glass into particles to form a frit glass having        the composition;    -   blending the frit glass with one or a more phosphors to form a        phosphor-frit glass mixture;    -   converting the phosphor-frit glass mixture into a paste by        adding at least one organic liquid to the mixture;    -   applying the paste onto a surface; and    -   firing the applied paste to burn out organic material to form a        phosphor-frit glass.

Another embodiment is a glass composition comprising in mole percent:

-   -   10-30% Bi₂O₃;    -   greater than 0% Na₂O;    -   15-50% ZnO, ZnF₂, or a combination thereof;    -   30-55% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   0-12% BaO, CaO, SrO, or combinations thereof.

Embodiments may have one or more of the following advantages: theconsolidated phosphor-containing glass layer and a device comprising theglass phosphor-containing layer are thermally more robust than when asilicone is used as the encapsulation material; the consolidatedphosphor-containing glass layer has better chemical and environmentalstability; there is a better refractive index match between theconsolidated phosphor-containing layer and the layer containing the LED,which reduces backscatter, the ability to maintain a quantum efficiencyof the phosphor in the glass of greater than 90% (e.g., greater than95%), the ability to make the composites at a thickness as small as 100um, the ability to maintain a processing temperature of less than about520° C. so as not to thermally degrade the phosphor, the capability ofcombining different phosphors into a single layer, the ability to makegeometric patterns of the phosphor on the substrate; the ability tocontrol the packaged LED color or white point; and/or since the phosphorplate is made as a separate piece, the optical thickness and emissioncolor can be measured before assembly, thus reducing the number ofreject LEDs. Further, the Pb-free encapsulant glasses can beindex-matched to the LED phosphors and can function as a sealing frit attemperatures below the upper use limit of the phosphors.

In related embodiments, a solid glass layer comprises a glass matrix andat least one phosphor dispersed throughout the matrix, wherein the glasscomprises Bi₂O₃ and at least 30 mol % B₂O₃.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments as described herein, including the detailed descriptionwhich follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understanding the natureand character of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiment(s), and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is an illustration of features of a device in which phosphorsencapsulated in a silicone materials are applied to and encapsulates aLED device in a vessel;

FIG. 2 is an illustration of features of a device in accordance withembodiments of the present disclosure in which a consolidatedphosphor-containing glass layer is formed by tape casting the glass fritmaterial mixed with one or a plurality of phosphors and firing thecasted phosphor-frit glass layer;

FIG. 3 is a graph comparing the total transmission spectra of tape castglass-phosphor films made from the same glass composition, but differentparticle size;

FIG. 4 is a graph showing thickness normalized absorbance as function ofwavelength for different glass frit-phosphor blends fired at differenttemperatures;

FIG. 5 is a plot of quantum efficiency versus the thickness-normalizedabsorbance peak height; and

FIG. 6 is a plot of quantum efficiency versus wavelength).

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments ofphosphor/frit glass materials and their use in LED articles, examples ofwhich are illustrated in the accompanying drawings. Whenever possible,the same reference numerals will be used throughout the drawings torefer to the same or like parts.

One embodiment is an article comprising a glass layer, wherein the layercomprises a glass comprising Bi₂O₃ and at least 30 mol % B₂O₃; and atleast one phosphor, wherein the layer is a fired mixture of a fritcomprising the Bi₂O₃ and B₂O₃ and the at least one phosphor, and whereinthe layer is Pb free.

Another embodiment is a method for making a glass article, the methodcomprising:

-   -   providing a glass composition comprising Bi₂O₃ and at least 30        mol % B₂O₃;    -   melting the composition and forming the melted composition into        a glass;    -   grinding the glass into particles to form a frit glass having        the composition;    -   blending the frit glass with one or a more phosphors to form a        phosphor-frit glass mixture;    -   converting the phosphor-frit glass mixture into a paste by        adding at least one organic liquid to the mixture;    -   applying the paste onto a surface; and    -   firing the applied paste to burn out organic material to form a        phosphor-frit glass.

Another embodiment is a method for making a glass article comprising:

-   -   providing a glass composition comprising Bi₂O₃ and at least 30        mol % B₂O₃;    -   melting the composition and forming the melted composition into        a glass;    -   grinding the glass into particles to form a frit glass having        the composition;    -   blending the frit glass with one or more phosphors to form a        phosphor-frit glass mixture;    -   milling the phosphor-frit glass mixture;    -   sieving the milled phosphor-frit glass mixture;    -   converting the milled and sieved phosphor-frit glass mixture        into a paste by adding at least one organic liquid to the        mixture;    -   applying the paste onto a surface; and    -   firing the paste to burn out the organic material.

In various embodiments, the layer is Pb free.

Another embodiment is a glass composition comprising in mole percent:

-   -   10-30% Bi₂O₃;    -   greater than 0% Na₂O;    -   15-50% ZnO, ZnF₂, or a combination thereof;    -   30-55% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   0-12% BaO, CaO, SrO, or combinations thereof.

The glass composition, according to some embodiments, comprises at least1% Na₂O.

The glass composition, according to some embodiments, comprises 15-50%ZnO.

The glass composition, according to some embodiments, comprises:

-   -   12-20% Bi₂O₃;    -   5-12% Na₂O;    -   20-30% ZnO;    -   38-52% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   1-12% BaO, CaO, SrO, or combinations thereof.

The glass composition, according to some embodiments, comprises:

-   -   14-16% Bi₂O₃;    -   5-11% Na₂O;    -   22-27% ZnO;    -   40-51% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   1-11% BaO, CaO, SrO, or combinations thereof.

The glass composition, according to some embodiments, has a refractiveindex of 1.81-1.83 at 473 nm and a glass transition temperature of 460°C. or less.

The article, according to some embodiments, comprises a glass comprisingin mole percent:

-   -   10-30% Bi₂O₃;    -   0-20% M₂O, wherein M is Li, Na, K, Cs, or combinations thereof;    -   0-20% RO, wherein R is Mg, Ca, Sr, Ba, or combinations thereof;    -   15-50% ZnO, ZnF₂, or a combination thereof;    -   0-5% Al₂O₃;    -   0-5% P₂O₅; and    -   30-55% B₂O₃.

The article, according to some embodiments, comprises a glasscomprising:

-   -   0-6 Li₂O;    -   0-20 Na₂O;    -   0-10 K₂O; and    -   0-3 Cs₂O.

The article, according to some embodiments, comprises a glasscomprising:

-   -   0-3 MgO;    -   0-3 CaO;    -   0-20 BaO; and    -   0-3 SrO.

The article, according to some embodiments, comprises a glass furthercomprising 0-5% TiO₂, ZrO₂, Ta₂O₅, MoO₃, WO₃, or combinations thereof.

The article, according to some embodiments, comprises a glass furthercomprising 0-15% SiO₂.

The article, according to some embodiments, comprises a glass furthercomprising 0-5% of one or more rare-earth dopants.

The article, according to some embodiments, comprises a glass comprising0-5% of Eu₂O₃.

The article, according to some embodiments, comprises a glass comprisingin mole percent:

-   -   10-30% Bi₂O₃;    -   greater than 0% Na₂O;    -   15-50% ZnO, ZnF₂, or a combination thereof;    -   30-55% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   0-12% BaO, CaO, SrO, or combinations thereof.

The article, according to some embodiments, comprises a glass comprisingat least 1% Na₂O.

The article, according to some embodiments, comprises a glass comprising15-50% ZnO.

The article, according to some embodiments, comprises a glasscomprising:

-   -   12-20% Bi₂O₃;    -   5-12% Na₂O;    -   20-30% ZnO;    -   38-52% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   1-12% BaO, CaO, SrO, or combinations thereof.

The article, according to some embodiments, comprises a glasscomprising:

-   -   14-16% Bi₂O₃;    -   5-11% Na₂O;    -   22-27% ZnO;    -   40-51% B₂O₃;    -   0-3% SiO₂;    -   0-1% WO₃;    -   1-11% BaO, CaO, SrO, or combinations thereof.

The glass can further comprise 0-5% TiO₂, ZrO₂, Ta₂O₅, MoO₃, WO₃, orcombinations thereof. The glass can further comprise 0-5% of one or morealkaline earth metals. The glass can also further comprise 0-25% SiO₂.

In some embodiments, the glass has a refractive index in the range offrom 1.8 to 1.9. The glass can have a glass transition temperature of460° C. or less. The difference in refractive index between the frit andthe at least one phosphor can be ≤0.20 (e.g., less than 0.2 or less than0.1) in some embodiments.

In one embodiment, the surface can be either a surface of a substrate orsurface of a carrier substrate, for example, a glass or tape,respectively. The article can further comprise a substrate having theglass layer disposed thereon. The CTE of the glass layer and thesubstrate can be within ±2×10⁻⁶ of each other.

In one embodiment, the substrate can be a glass substrate. The glasssubstrate can have a thickness of 5 mm or less, for example, 4 mm orless, for example, 3 mm or less, for example, 2 mm or less, for example,1 mm or less, for example, 0.5 mm or less. The glass substrate can be athin flexible glass substrate.

In one embodiment, the carrier substrate can be a tape or substrate inwhich the glass layer can be removed from after it is made. The glasslayer can be removed from the carrier and then attached to anothersurface after fabrication and also fired on its own. The glass layer canhave a thickness of 5 mm or less, for example, 4 mm or less, forexample, 3 mm or less, for example, 2 mm or less, for example, 1 mm orless, for example, 0.5 mm or less, for example, 0.4 mm or less, forexample, 0.3 mm or less, for example, 0.2 mm or less, for example, 0.1mm or less, for example, 0.09 mm or less, for example, 0.08 mm or less,for example, 0.07 mm or less, for example, 0.06 mm or less, for example,0.05 mm or less. In some embodiments, the glass layer has a thickness offrom 0.01 to 1 mm, for example, from 0.01 mm to 0.2 mm.

The glass layer, on the substrate or alone, can be used to fabricate LEDlights in for example, fabrication processes such as wafer sizedprocesses, for example, 6 inches by 6 inches or even larger. MultipleLEDs can be fabricated on the glass layer and separated into single LEDsafter fabrication.

In an embodiment one or more phosphors are mixed with a glass fritmaterial (the encapsulating material) to form a phosphor-frit glassmixture, and then applied to an LED, for example, a GaN or InGaN LED,within a vessel. In FIG. 2, which is similar to FIG. 1, a phosphor 114(illustrated as circular dots) has been mixed with a glass frit material116 to form a phosphor-frit glass mixture which is fired to create aglass sheet having a phosphor embedded into it. In addition, package 120shown in FIG. 2 illustrates the LED 110, wire bonds 112 and packagesubstrate 118 and the vessel or cup 122. The phosphor-containing fritglass mixture (114,116) can also be applied to a substrate usingstandard paste processes, by a screen printing, or by spraying, followedby firing to produce a dense glass layer, the phosphor/frit layer,overlying the foregoing substrate. Since the fired phosphor-containingfrit mixture is a glass, a cover lens may not be required. Thisdisclosure is directed to the preparation, application, and thermalprocessing of the mixed frit/phosphor materials in the form shown inFIG. 2. The disclosure further includes a choice of frit glasscompositions that can be used to provide the correct thermalcharacteristics while being consistent with the addition of the phosphorand its application to an appropriate glass substrate.

In various embodiments, the Bi-containing borate glasses are envisagedto be used as encapsulating frits in either of two methodologies. In onecase, a mixture of powdered glass and phosphor, blended with a suitableorganic binder, dispersant and solvent, is screen printed onto a thin,high thermal expansion coefficient glass substrate. Examples of thesubstrate include any of the high Na content aluminosilicate glassesthat Corning manufactures via the fusion process. Screen printingtypically involves the deposition of multiple layers in order to buildup a phosphor-frit layer of sufficient thickness. The substrate/fritassembly is then fired at ˜350° C. in order to burn off the organicconstituents of the paste, and then subsequently heated to 500-550° C.to sinter the frit to a sufficiently transparent state. In embodiments,the binder can be fully removed or substantially removed from the glasscomposition prior to sintering. As such, the temperature at which binderburnout occurs can be less than the sintering temperature. In furtherembodiments, the loading of phosphor in the sintered glass can rangefrom about 1 to 30 vol. %, e.g., 1, 2, 5, 10, 15, 20 or 30 percent byvolume. In order to avoid reduction of Bi, the sintering may be carriedout in an O₂-enriched atmosphere rather than air. Exemplary glasses 15,10, 29, 31, 71, 84 and 97 from the tables have been processed in thisfashion to yield an encapsulated phosphor layer of sufficienttransparency (e.g., at least 60% or at least 70%).

In another embodiment, a free-standing frit/phosphor film is made by atape casting procedure. Exemplary glass sample 29 and Ce:YAG phosphorpowders were jet milled to d50 of <5 um. A tape casting slip wasprepared by mixing the powders in a proportion of 85 volume % exemplaryglass 29 and 68 (from the Tables below) and 15 volume % Ce:YAG in ethylacetate solvent with Emphos PS-236 dispersant and polypropylenecarbonate binder. Slip was cast using a 22-mil draw-down blade on tefloncarrier film. The tape was dried, released and sintered at 550° C. inair. The sample remains substantially glassy after such treatment.Polypropylene carbonate was chosen as binder as we found it critical toemploy a binder which burns out at <300° C. in order to prevent trappingof organics in the sintered glass matrix. The tape was sintered on afibrous alumina setterboard with alumina felt as a cover. The fibrousboard limits bonding of the glass to the setter during firing. Precisedimensioned parts were cut from the sintered tape using an ablativelaser cutting system with an Nd:YVO4 laser at 355 nm. The finalthickness of the Ce:YAG in glass sample was 100 um, though thicknessesin the range of 50 to 250 microns are contemplated.

Casting uniformity was improved with polypropylene carbonate (PPC)binder using a solvent system comprising dimethylcarbonate (DMC) andpropylene glycol diacetate (PGD). Of the relatively limited set ofsolvents known to solubilize PPC, DMC and PGD are advantageous in thatthey are relatively non-toxic, readily dissolve PPC and the solventevaporation rate can be tuned by adjusting the proportion of PGD (lowvolatility) to DMC (high volatility).

A smooth setter board is advantageous to improve the surface finish ofthe fired composite. The glass compositions described herein fire at arelatively low temperature of about 600° C. or less. At thistemperature, stainless steel setter boards with a smooth surface may beused. Lower firing temperature can eliminate or substantially minimizethe issue of glass reaction with the phosphor particle.

The particle size distribution of the glass frit may be instrumental inachieving good optical performance, especially high quantum efficiency.Much improved performance is found if the glass powder average particlesize is above about 10 um. It is believed larger glass particle sizemitigates reduction of Bi₂O₃ contained in the glass during sintering ofthe glass/phosphor composite. Composites made with a glass having aparticle size distribution d50 under 1 um are less transparent thancomposites made with the same glass at a d50 of over 1 um, for example,over 10 um. It is also anticipated that, in the case of a YAG-basedphosphor, which has similar density to the glass compositions describedherein, that the particle size be similar to reduce segregation of theglass and phosphor particles during drying of the green tape.

FIG. 3 is a graph comparing the total transmission spectra of tape castglass-phosphor films made from the same glass composition, but differentparticle size. The glass composition is summarized in Example 76 (fromthe Tables below) with Ce:YAG phosphor particles. The films were firedunder the same conditions, and produced dense, self-supporting filmswhich were ˜100 um thick. Particle size is indicated by the conventional“d50” measurement which indicates the size where 50% by volume of theparticles are below the indicated size. The data clearly show membranesmade with submicron glass powder show browning of the glass whichreduces transmission, especially in the region near 400 nm, whichinterferes with the Ce:YAG phosphor absorption peak centered near 450nm. Lines 26, 28, and 30 show d50=0.81 um, d50=3.55 um, and d50=15.85um, respectively. The film fabricated from glass at d50=15.85 ummeasured a quantum efficiency of 97%. It is desirable to achieve aquantum efficiency of over 90%, more preferably 95% or more.

High performance membranes can be obtained with a volume fraction ofphosphor in the range of 1% to 30%, for example, in the 5% to 30% range.Higher phosphor content allows for a higher sintering temperature, butrequires a thinner film for optimal color point. Film thickness can bein the range of 30 to 1000 um, for example, 50 to 300 um, for example,75 to 200 um.

In the case of Ce:YAG phosphor of conversion of blue LED light to whitelight, in order to achieve a desirable color point for converting blueLED to white light, the volume fraction of phosphor required variesinversely with film thickness, and can be described by the following:Vf=a/t, wherein Vf is expressed in % and t is in um, the constant a,with units um-%. Vf can be in the range of 1000 to 2000. For example fora film thickness of 100 um, the phosphor volume fraction can be in therange of 1000/100% to 2000/100% or 10% to 20%.

In various embodiments, one or both of the film thickness and the amountof the phosphor loading can be controlled in order to affect the colorpoint of the glass layer.

EXAMPLE

A free-standing glass-phosphor composite was produced as follows:Drigaged exemplary glass 76 (from the Tables below) was dry ball-milledand sieved at −400 mesh to achieve a particle size distribution withd50=15.85 um. Commercially available Ce:YAG phosphor powder with d50=14um was added to the glass powder in a 85 vol % glass/15 vol % phosphorratio. PPC binder and a 50/50 solvent mix of DMC and PGD were added inthe weight fractions shown in the below table. A commercial dispersantmade by BYK company, Dispersbyk-142, was used. The ingredients weremixed in a planetary mixer to achieve a uniform tape casting slip. Slipwas cast using a conventional 18-mil gap doctor blade on a Teflon-coatedMylar carrier film. After drying the cast green tape was released, cutto size and sintered on a stainless-steel setter board at 510° C. for 2hours. At this temperature acceptable density and optical quality isachieved while minimizing the possibility of either excessive stickingof the part to setter board, or loss of dimensional tolerance throughexcessive glass flow which can occur at sintering temperature as littleas 10° C. higher. Since the glass viscosity decreases exponentially withincreasing temperature, furnace uniformity is critical. It is desirableto fire the part in a furnace with thermal gradient across the part lessthan 20° C., more preferably less than 10° C., most preferably less than5° C. After firing, a part with precise dimensions was laser cut out ofthe fired casting to produce a 10 cm×10 cm part with a uniform thicknessof 100+/−2 um. Quantum efficiency was measured at 97%. Table 1 shows theexemplary components and weight fractions.

TABLE 1 Component Weight fraction Exemplary glass 76 0.545 Ce:YAGphosphor 0.095 Polypropylene Carbonate 0.041 Dispersbyk-142 0.005Propylene Glycol Diacetate 0.157 Dimethyl Carbonate 0.157

FIG. 4 is a graph showing absorbance normalized to thickness (A/t) ofcomposite glass/phosphor films as a function of wavelength. The quantumefficiency (QE) of composite glass/phosphor films is related to measuredtransmission spectra. In particular it is desirable to produce aglass-phosphor composite, where the phosphor is for example, Ce-dopedYAG, wherein the transmission of the glass component is as high aspossible in the blue range, namely 400 to 500 nm range. In this way, themaximum quantum efficiency can be achieved as the phosphor absorbssubstantially all the available photons capable of exciting fluorescencein the phosphor. In particular, the correlation of quantum efficiencyand the thickness-normalized absorbance peak height 32 (in FIG. 4) isshown in FIG. 5 and the correlation of quantum efficiency and thewavelength of the local minima in A/t 34 (in FIG. 4) is shown in FIG. 6,both figures demonstrating the good correlation of absorbance data toQE. In embodiments, the wavelength of the A/t minimum can be below about416 nm to achieve a quantum efficiency of over 90%. Similarly, the A/tpeak height as shown generally exceeds 1 to achieve quantum efficiencyover 90%.

Exemplary glasses are shown in Tables 2-14, where compositions are givenin terms of mol %. Tg, Tx, α300 refer to the glass transitiontemperature (over the range of 25° C. to 300° C.), temperature of theonset of crystallization, thermal expansion coefficient at 300° C.,respectively. Softening point refers to the temperature at which theglass viscosity is Log 10^(7.6). n473, n532, n633 refer to therefractive index measured at 473 nm, 532 nm, and 633 nm, respectively.

TABLE 2 Examples Mol % 1 2 3 4 5 6 7 8 Bi₂O₃ 20 20 22.5 22.5 20 20 25 20Li₂O 2.5 Na₂O 10 10 5 10 10 10 20 K₂O 2.5 ZnO 40 30 27.5 27.5 30 30 2520 B₂O₃ 40 40 40 40 37.5 35 40 40 P₂O₅ 2.5 5 Tg 433 417 411 389 407 425403 357 Tx 580 566 555 569 492 n473 1.935 1.963 n532 1.914 1.94 n6331.892 1.917

TABLE 3 Examples Mol % 9 10 11 12 13 14 15 16 Bi₂O₃ 20 20 20 20 20 2017.5 20 Na₂O 10 10 15 K₂O 10 ZnO 20 20 45 35 20 30 32.5 25 BaO 20 10 10B₂O₃ 40 40 35 45 40 50 40 40 Tg 421 394 415 439 366 449 422 388 Tx 570539 n473 1.906 n532 1.903 1.886 n633 1.882 1.867

TABLE 4 Examples Mol % 17 18 19 20 21 22 23 24 Bi₂O₃ 20 15 15 15 15 1513 13 Li₂O 5 5 5 Na₂O 10 15 15 10 10 15 10 ZnO 30 30 25 30 30 25 27 27BaO 10 10 10 5 5 10 10 10 B₂O₃ 40 35 35 35 35 35 35 35 Tg 435 402 379385 377 373 387 379 Tx 530 526 456 472 543 458 α300 103 116 115 n473n532 1.843 1.819 n633 1.825 1.8025

TABLE 5 Examples Mol % 25 26 27 28 29 30 31 32 Bi₂O₃ 17 17 15 15 16 2016 15 Li₂O 5 Na₂O 15 10 15 15 10 5 5 10 ZnO 23 23 12.5 21.3 25 26.5 21.3ZnF₂ 12.5 25 BaO 10 10 10 10 10 10 10 10 B₂O₃ 35 35 35 35 42.7 40 42.543.7 Tg 377 367 363 355 412 421 439 427 Tx 528 469 α300 119 115 n5321.867 1.852 1.927 1.875 n633 1.847 1.835 1.906 1.8575 Softening 484.9point

TABLE 6 Examples Mol % 33 34 35 36 37 38 39 40 Bi₂O₃ 16 16 16 16 16 1615 16 Li₂O 5.25 1.75 Na₂O 6 2.5 2 1.75 5 3.5 2.1 2.8 K₂O 3.75 1.25 2 42.4 3.2 Cs₂O 2.5 1.25 2.5 2.5 1.5 2 ZnO 23.5 26.5 26.5 26.5 26.5 23.526.5 23.5 BaO 10 2.5 10 7.5 5 2.5 2.5 Al₂O₃ 3 B₂O₃ 42.5 42.5 50 42.542.5 45.5 50 50 Tg 409 433 459 427 423 409 447 434 Tx 582 α300 n473 n5321.826 1.852 1.848 1.851 1.851 n633 1.81 1.835 1.83 1.834 1.834 density4.901 Softening 515.1 point

TABLE 7 Examples Mol % 41 42 43 44 45 46 47 48 Bi₂O₃ 15.5 15 15.5 14 1414 14 14 Na₂O 1.925 2.1 3.5 10.8 10.8 5.8 10.8 10.8 K₂O 2.2 2.4 4 5 Cs₂O1.375 1.5 2.5 ZnO 26.5 28.5 26.5 21.5 26.5 21.5 21.5 16.5 BaO 10 8 5.510.7 10.7 10.7 15.7 15.7 B₂O₃ 42.5 42.5 42.5 43 38 43 38 43 Tg 425 427406 417 407 410 403 411 Tx 536 α300 n473 n532 n633 softening 494.3 point

TABLE 8 Examples Mol % 49 50 51 52 53 54 55 56 Bi₂O₃ 14 14 14 13 15 1515 15 Na₂O 5.8 5.8 5.8 10.9 13.7 10 10 13.7 K₂O 5 5 5 ZnO 16.5 26.5 21.521.8 21.3 21.3 21.3 21.3 BaO 15.7 10.7 15.7 10.8 10 13.7 10 13.7 B₂O₃ 4338 38 43.5 40 40 43.7 36.3 Tg 409 404 403 420 419 424 428 404 Tx 516α300 n473 1.8636 n532 1.8675 1.8485 n633 1.8486 1.8302

TABLE 9 Examples Mol % 57 58 59 60 61 62 63 64 Bi₂O₃ 15 15 15 15 12 1515 15 Na₂O 10 10 11 10 10 10 10 10 ZnO 20 15 18 20 33 29.8 27.3 22.3 BaO10 10 6 15 15 2.5 5 10 B₂O₃ 45 50 50 40 30 42.7 42.7 42.7 MoO₃ 0.5 Tg415 428 414 429 426 419 Tx α300 9.39 n473 1.8815 1.8726 1.8628 n5321.8634 1.8566 1.8463 n633 1.8469 1.8392 1.829

TABLE 10 Examples Mol % 65 66 67 68 69 70 71 72 Bi₂O₃ 15 15 15 15 15 1515 15 Na₂O 10 10 10 8 10 10 10 10 ZnO 22.3 22.3 22.5 24.5 22.3 22.3 22.322.3 BaO 10 10 2.5 2.5 10 10 10 10 B₂O₃ 42.7 42.7 50 50 40.2 37.7 42.732.7 WO₃ 0 1 0.5 0.5 0 0 0 0 MoO₃ 1 0 0 0 0 0 0 0 SiO₂ 0 0 0 0 2.5 5 010 Tg 421 421 443 454 422 424 419 424 Tx α300 8.5 10.2 9.95 10.09 n4731.8579 1.8607 1.8441 1.8605 1.8438 1.8559 n532 1.8415 1.844 1.82821.8438 1.8272 1.8392 n633 1.8245 1.8269 1.8125 1.8269 1.812 1.8229density 4.967 4.988 Softening 519.3 495.3 496.6 493.3 499.3 point

TABLE 11 Examples Mol % 73 74 75 76 77 78 79 80 Bi₂O₃ 15 15 15 15 15 1515 15 Na₂O 10 8 8 8 8 0 0 8 ZnO 21.3 22.3 22.5 24.5 27 20 25 22 BaO 8 84.5 2.5 0 15 10 2.5 B₂O₃ 40.7 41.7 48 48 50 50 50 50 SiO₂ 5 5 2 2 2.5 50 0 MgO 0 0 0 0 0 0 0 2.5 Tg 430 440 451 453 456 467 472 455 Tx α3009.59 9.27 8.52 8.24 8.73 7.97 n473 1.8575 1.8681 1.8548 1.8393 1.85651.8559 1.8361 n532 1.8408 1.8505 1.8381 1.8245 1.8415 1.841 1.8208 n6331.8239 1.8333 1.8216 1.8086 1.8258 1.825 1.8046 density 4.812 Softening503.5 511 519.1 point

TABLE 12 Examples Mol % 81 82 83 84 85 86 87 88 Bi₂O₃ 15 15 15 15 15 1515 15 Na₂O 6 10 10 10 8 10 10 10 ZnO 26.5 22.3 20.3 20.3 25 22.3 22.322.3 BaO 2.5 10 10 12 11 10 10 10 B₂O₃ 50 42.7 42.7 42.7 41 42.7 42.742.7 SiO₂ 0 0 2 0 0 0 0 0 Eu₂O₃ 0 0 2 0 0 1.5 0.5 0.15 Tg 458 422 424420 425 426.5 425 423 Tx 519 α300 8.12 9.81 9.99 10.27 10.01 n473 1.84571.8552 1.8496 1.8545 1.8662 n532 1.8307 1.8385 1.8331 1.838 1.8495 n6331.8159 1.8217 1.8169 1.8213 1.8322

TABLE 13 Examples Mol % 89 90 91 92 93 94 95 96 Bi₂O₃ 15 14.5 14.5 14.514.5 15 14 14 Na₂O 10 10 10 10 10 10 10 10 ZnO 20 21.8 22 21.9 21 22.322.3 22.3 BaO 7 8 8.8 8.4 7.8 2 7 4 B₂O₃ 41 42.7 42.7 42.7 42.7 42.742.7 42.7 SiO₂ 0 0 0 0 0 0 0 0 Eu₂O₃ 7 3 2 2.5 4 4 4 4 Tg 443 439 430434 437 443 440 444 Tx 585 α300 9.11 9.61 9.14 n473 1.8779 1.8621 1.8651n532 1.8611 1.8459 1.8487 n633 1.8447 1.8299 1.8328

TABLE 14 Examples 97 98 99 100 101 Mol % Bi₂O₃ 13.5 15 15 15 15 Na₂O 106 6 6 6 ZnO 22.3 26.5 26.5 26.5 26.5 BaO 8 1.25 0 0 0.5 SrO 1.25 2.5 0 1CaO 0 0 2.5 1 B₂O₃ 41 50 50 50 50 Eu₂O₃ 4 Tg 441 462.2 462.2 463.3 463.3Tx α300 9.6 n473 1.8575 n532 1.8423 n633 1.8261

The disclosure is directed to glass containing at least one phosphor;and to a process whereby a phosphor powder, or plurality of differentphosphor powders, is combined with a suitable fritted glass material,the “frit glass”, and a liquid organic vehicle (for example withoutlimitation, terpineol, ethylcellulose with dispersants and surfactants)to form a frit paste. The paste is then deposited on a compatiblesubstrate (a substrate whose CTE is matched to within 2×10⁻⁶/° C. of thefrit glass), for example without limitation, by screen printing orspraying, (screen print, or spray) and then heated to a suitable firsttemperature to drive of the organic vehicle and then heated to a highersecond temperature to consolidate the phosphor/frit glass mixture into adense phosphor-containing glass. The phosphor may comprise quantum dots,for example, quantum dots having a particle size ranging from 1 to 10nm.

The first temperature is for driving off the organic vehicle and it isdetermined by, for example, the boiling point of the organic vehicle orthe use of vapor pressure data and can be carried out at atmosphericpressure or under vacuum. The second higher temperature that is used toconsolidate or fire the phosphor/frit glass mixture into a dense glassis determined by the frit material, with the provision that thesoftening temperature of the substrate to which the phosphor/frit glassmixture is applied has to be at least 100° C. higher than theconsolidation or firing temperature of the phosphor/frit glass mixture.This phosphor/frit glass mixture can be applied as a layer on oradjacent to the active plane of a LED device. The amount of phosphorpowder in the phosphor/frit glass mixture can be varied to the desiredamount. The ultimate thickness of the consolidated phosphor-contain fritlayer can be increased by a plurality of depositions of thephosphor/frit glass mixture.

In various embodiments, the phosphor powder can be homogeneouslydistributed throughout the glass. In further embodiments, thedistribution of phosphor powder can be localized within the glass, i.e.,at one or both of the free surfaces of the glass layer.

The phosphor-containing frit glass mixture materials are different fromthe same frit material without the phosphor. Specifically, the additionof a specific phosphor phase to the frit material alters the rheologicalproperties of the resulting phosphor-frit glass paste and the subsequentconsolidation thermal treatment. The consolidation thermal treatmentmust be such that it does not degrade the fluorescent property of thephosphor. This is an important factor in the choice of the frit glassand the subsequent processing. It is the appropriate finding of thiscombination of the properties, namely the frit glass composition, theparticular phosphor material and the glass substrate, that constitutevarious embodiments of the instant disclosure. Because of thetemperature limitation of the phosphor-frit glass material and thepotential for degradation of certain phosphor materials, for example,Ce/YAG, or for reaction between frit glass and the phosphor materials,embodiments relate to the use of frit materials whose sinteringtemperature or flowing temperature is sufficient low such that thephosphors present in a phosphor-frit mixture are not degraded. Theresult of this restriction is that higher CTE frit materials aretypically used, which can, in turn, impact the choice of the substrateglass so that the CTE of the phosphor-containing frit glass formed byfiring a phosphor-frit glass mixture will match the substrate CTE.

Phosphor materials are commercially available from Beijing Yugi Science& Technology Co. Ltd. (Beijing, China), Shanghai Keyan PhosphorTechnology Co. Ltd (Shanghai, China) and Litec-LLL GmbH (Greifswald,Germany); and have also been described in patents and technicalliterature, for example, U.S. Pat. Nos. 6,572,785 and 7,442,326, and W.J. Park et al., “Enhanced Luminescence Efficiency for Bi, Eu doped Y ₂ O₃ Red Phosphors for White LEDs,” Solid State Phenomena, Vols. 124-126(2007), pages 379-382, and Rong-Jun Xie et al., “Silicon-basedoxynitride and nitride phosphors for white LEDs—A review,” Science andTechnology of Advanced Materials 8 (2007), pages 588-600.

As indicated above, FIG. 1 is a drawing of a white light LED in atypical surface mount package, FIG. 1 illustrates the LED 10, wire bonds12, phosphor particles 14 (illustrated as circular dots) in a siliconematerial 16 surrounding phosphor particles 14, a substrate 18 and apackage 20 for a LED, for example, an Marubeni SMTW47 InGaN LED(http://tech-led.com/data/L850-66-60-130.pdf). The package 20 comprisesa substrate 18, an epoxy resin lens 24, and a vessel or cup 22 made fromwhite plastic or ceramic to contain the silicone-phosphor mixture,protect the LED, and to reflect the light from the package. In FIG. 2, aphosphor 114 (illustrated as circular dots) has been mixed with a glassfrit 116 to form a phosphor/frit glass mixture and fired to create aglass sheet. In addition, FIG. 2 illustrates the package 120, whichcomprises the LED 110, wire bonds 112 and package substrate 118 and thevessel or cup 122. The phosphor/frit glass mixture material (114,116)can also be applied to a substrate using standard paste processes, by ascreen printing, or by spraying, followed by firing to produce a densephosphor/frit glass layer overlying the substrate. As a result ofincorporating the phosphor into a glass layer numerous advantages areobtained over the practice of mixing the phosphor into a silicone orepoxy material.

In particular, the phosphor/frit glass layer and the resulting deviceoverall are thermally more robust than when a silicone is used as theencapsulation material, and the phosphor/frit glass layer has betterchemical and environmental stability. For example, one can incorporatered and yellow phosphors into a single frit glass blend. Since thephosphor/frit glass blend can be formed into a “paste” of varyingfluidity, the blends are suitable for thick film application to theactive plane. Example liquids used to form the blend include varioussolvent mixtures, including a mixture of propylene glycol diacetate anddimethyl carbonate. Other advantages include (1) reduced backscatterbecause the frit glass material can be chosen so that there isphosphor/frit glass materials achieve a better refractive index matchbetween the phosphor and the frit glass and the layer containing thepn-junction (the LED); and (2) the ability to make geometric patterns ofthe phosphor on the substrate. Finally, the use of the phosphor/fritglass blend imparts the ability to control the packaged LED color orwhite point. Since the phosphor-containing plate is made as a separatepiece, the optical thickness and emission color can be measured beforeassembly, thus reducing the number of reject LEDs.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

We claim:
 1. A method for making a glass article comprising: providing aglass composition comprising Bi₂O₃ and at least 30 mol % B₂O₃; meltingthe composition and forming the melted composition into a glass;grinding the glass into particles to form a frit glass having thecomposition; blending the frit glass with one or a more phosphors toform a phosphor-frit glass mixture; converting the phosphor-frit glassmixture into a paste by adding at least one organic liquid to themixture; applying the paste onto a surface; and firing the applied pasteto burn out organic material to form a phosphor-frit glass.
 2. Themethod according to claim 1, further comprising cooling the firedphosphor-frit glass to room temperature after the firing.
 3. The methodaccording to claim 1, wherein the firing comprises firing the appliedpaste in air to a temperature of approximately 350° C. at a temperatureramp rate of 2° C./min and holding the paste at approximately 350° C.for 1 hour to burn out the organic material.
 4. The method according toclaim 1, wherein the firing comprises firing the applied paste in air toa selected temperature in the range of 475-600° C. at a temperature ramprate of 2° C./min and holding the applied paste at the selectedtemperature for 2 hours.
 5. The method according to claim 1, wherein theapplying comprises screen printing or tape casting the paste onto thesurface.
 6. The method according to claim 1, wherein the blendingcomprises mixing the frit glass and the one or more phosphors with asolvent mixture comprising propylene glycol diacetate and dimethylcarbonate.